open-port barfs on a port that was just closed

With a config-changed hook:

    #!/bin/sh

    . /etc/default/bitlbee

    # Close the old port
    echo "Closing old port $BITLBEE_PORT"
    close-port "$BITLBEE_PORT/tcp"

    PORT=`config-get port`

    echo "Opening new port $PORT"

    cat >/etc/default/bitlbee<<EOF
    BITLBEE_PORT=$PORT
    BITLBEE_OPTS="-F"
    BITLBEE_DISABLED=0
    BITLBEE_UPGRADE_DONT_RESTART=0
    EOF

    /etc/init.d/bitlbee restart

    open-port "$PORT/tcp"

the open-port throws the attached exception if it's opening the same port it just closed.
Net result is no ports open.